1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting a signal in a wireless communication system.
2. Discussion of the Related Art
FIG. 1 is a diagram illustrating the configuration of an exemplary wireless communication system.
Referring to FIG. 1, a wireless communication system 100 includes a plurality of Base Stations (BSs) 110a, 110b and 110c and a plurality of User Equipments (UEs) 120a to 120i. The wireless communication system 100 may include homogeneous networks or heterogeneous networks. Heterogeneous networks refer to networks in which different network entities coexist, such as a macro cell, a femto cell, a pico cell, a relay station, etc. A BS is usually a fixed station that communicates with UEs. Each BS 110a, 110b or 110c provides services to its specific geographical area 102a, 102b or 102c. For the purpose of improving system performance, the specific service area of the BS may further be divided into a plurality of smaller areas 104a, 104b and 104c. These smaller areas may be called cells, sectors or segments. In an Institute of Electrical and Electronics Engineers (IEEE) 802.16 system, cell Identities (IDs) (Cell_IDs or IDCells) are assigned from the perspective of a whole system, whereas sector IDs or segment IDs are assigned from the perspective of the service coverage of each BS, ranging from 0 to 2. The UEs 120a to 120i, which are mobile or fixed, are generally distributed over the wireless communication system 100. Each UE may communicate with at least one BS on a downlink and an uplink at a point of time. The communication may be conducted in Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Single Carrier-FDMA (SC-FDMA), Multi Carrier-FDMA (MC-FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), or a combination of them. Herein, a downlink refers to a communication link directed from a BS to a UE and an uplink refers to a communication link directed from the UE to the BS.
FIG. 2 illustrates an exemplary channel change in frequency in the wireless communication system.
Referring to FIG. 2, if a system band has a bandwidth greater than a coherence bandwidth, a channel may fluctuate greatly in the system band. Then a frequency diversity gain may be achieved by spreading a transmission signal across all or part of the system band along the frequency axis. For example, allocation of frequency resources to the transmission signal by appropriate permutation may lead to mixing and spreading of the transmission signal across a predetermined bandwidth. Accordingly, there exists a continuous need for a permutation scheme to effectively distribute a transmission signal across a predetermined bandwidth.